A.As long as the class finished, the students ran out, screamed and shouted.
B.No sooner did the class finish than the student ran out, screamed and shouted.
C.As soon as the class had finished, the student ran out, screamed and shouted.
D.If the class was over, the students would run out, scream and shout.

A.I couldn’t understand his book because I didn’t read it.
B.I wouldn’t have understood what he was saying if I hadn’t read his book.
C.I was had to understand his book so I didn’t understand what he was saying.
D.If I had read his book, I would have understood what he was saying.

A.I couldn’t understand his book because I didn’t read it.
B.I wouldn’t have understood what he was saying if I hadn’t read his book.
C.I was had to understand his book so I didn’t understand what he was saying.
D.If I had read his book, I would have understood what he was saying.

A.wear a backpack
B.praise yourself
C.criticize yourself
D.check up your back

A.wear a backpack
B.praise yourself
C.criticize yourself
D.check up your back

A.produce
B.bring out
C.form
D.terminate

A.the cells and tissues of the brain.
B.the resident memory.
C.the mobility of the mind and the body.
D.the arteries of the brain.

A.the cells and tissues of the brain.
B.the resident memory.
C.the mobility of the mind and the body.
D.the arteries of the brain.

A.only use mobile phones in medical emergencies.
B.keep off mobile phones regularly.
C.never use mobile phones in all cases.
D.only use mobile phones in urgent cases.

A.their invisible rays.
B.their raiding power.
C.their radiant light.
D.their power of attraction.